The language Mr. Trump uses, his willingness to insult, his refusal to follow the standard conventions of polite society or decency — his crudeness — is not a superficial sideshow. It is his defining trait, both a rebuke of Madison’s experiment and a giveaway that he is a demagogue.

Look for the common thread in his otherwise unconnected actions: Associating ordinary immigrants with rapists and murderers was not necessary to demonstrate a commitment to lowering crime or saving American jobs; it was a way of showing he would say what others would not. Tearing a mask off on the White House balcony did not help the economy; it was a declaration of independence from the rule of experts. Trolling the media on whether to accept the results of the election; refusing to offer, on a journalist’s command, the requisite statement opposing white nationalists; and declining to apologize as if backing down would compromise his principles — these are positions whose substance should not be ignored, and I find them morally appalling — but we understand the fundamental political dynamic better when we focus less on their content and more on their motivation: He is determined to show that he will not be shamed.

To allow oneself to be shamed is to admit that you are subject to and ruled by society’s arbiters of what is acceptable. Demagogues, as a rule, insist that they will not be so ruled; that is part of their democratic appeal. Shame is a constraint, and so is an affront to freedom.